Foundry operations use molds in which to make various structures from molten metallic materials. Molds are made from many materials such as plastics, metals, sand and clay with binders like benenite. Sand, however, generally constitutes the predominant material used by the foundry industry. The art of fabricating molds is extremely old, and until recent years, comprised the traditional steps of fashioning the mold pattern from a mixture of sand and moist clay and baking at least the mold core at elevated temperatures to harden the mold. Frequently, the molds need not only large quantities of sand to provide sufficient strength to hold their shape during the pouring process, but also require a backup with steel forms known as flasks.
The foundry industry has recently developed a new mold fabrication process which utilizes granular sand and a binder. Briefly, the binder and sand are mixed, fashioned into a desired pattern, and thereafter the binder chemically reacts and hardens to form the mixture into a mold. Other than eliminating the need to bake the mold, another readily observable advantage is the increased strength of the mold relative to conventional molds. Less sand per unit volume of the mold is also needed. The use of flasks is virtually eliminated.
Reclaimation of molding sand following use of the mold has always been a matter of concern and, because of economics, necessary. The cost of replacing or disposing of the sand is high. With the older or conventional molds, the technique employed was simple. It was expedient only to screen out the trash and break the mold. Ring breakers on a vibrating screen were often employed.
The later techniques using sand and chemical binders for mold fabrication, however, complicated the reclaiming procedure. The binder is very hard and surrounds virtually every grain of sand and must be removed if the sand is to be reclaimed. As stated above, the economics of replacement and disposal of the sand dictate the need for reclaimation. Presently, there are two techniques which have been employed: a mechanical abrading technique of the sand to remove the binder and a thermal reclaimation. The latter has often been termed too expensive as it requires heating of the sand to temperatures in excess of 700.degree. Celsius with subsequent cooling.
Mechanical abrading may be accomplished, for example, by feeding the sand into a high speed centrifugal wheel and impacting on a surface. This shot-blast technique has been considered successful. There are other techniques such as for example, U.S. Pat. Nos. 3,793,780 and 4,025,419 both of which describe a vibratory tumbling apparatus which through material abrasion of foundry lumps causes a wearing down of the molds into particulate form. Specifically, both inventions through the geometry of the hopper, positioning of vibratory motors, and selective energization of the motors provides controlled directional movement to the lumps and/or sand. In one mode of operation, the lumps are retained in a desired area of the vibrating hopper. A second mode provides movement of the particulate material out of the hopper toward the reclaiming stage.
A disadvantage of the systems typified by the above is the small "through-put". The need to continually change the direction of flow provides an interval in which the throw of the hopper prevents the material to be reclaimed from exiting the hopper. Additionally, many of the lumps encountered are on the order of 45 to 60 centimeter cubes which would require an inordinate amount of time to wear down. Finally, when the hopper becomes filled with tramp material, it is necessary to reverse the direction of the various motors to cause the tramp material to move out of the hopper in the direction from which it was initially introduced.
It is therefore a paramount object of the present invention to provide unitary apparatus which in a continuous operation breaks up large mold lumps into smaller pieces which self-abrade under vibratory action into reclaimable particulate material. Still another important object is the elimination of periodic reversal for removal of tramp material.